In chronically SIV-infected RMs (day > 180), the percentage of CD4 T cells dropped to 32.6% ± 8.1%, whereas in terms of CD4 T cell counts, three RMs (PB023, PB028, and #1222) showed lower numbers, due to a lymphopenia, particularly in colic MLNs (1.95 × 107, 5.3 × 107, and 8.7 × 107, respectively), which is tenfold lower compared to that observed from the other SIV-infected RMs (PB013, 1.3 × 109; PB044, 6.6 × 108; #2012, 5.2 × 108; #2070R, 6.9 × 108). The gene discussed is CD4; the disease is lymphopenia.